A new Swift video series exploring functional programming and more.

#39 • Monday Nov 26, 2018 • Subscriber-only

Witness-Oriented Library Design

We previously refactored a library using protocols to make it more flexible and extensible but found that it wasn’t quite as flexible or extensible as we wanted it to be. This week we re-refactor our protocols away to concrete datatypes using our learnings from earlier in the series.

#38 • Monday Nov 19, 2018 • Subscriber-only

Protocol-Oriented Library Design: Part 2

With our library fully generalized using protocols, we show off the flexibility of our abstraction by adding new conformances and functionality. In fleshing out our library we find out why protocols may not be the right tool for the job.

#37 • Monday Nov 12, 2018 • Subscriber-only

Protocol-Oriented Library Design: Part 1

Perhaps the most popular approach to code reuse and extensibility in Swift is to liberally adopt protocol-oriented programming, and many Swift libraries are designed with protocol-heavy APIs. In today’s episode we refactor a sample library to use protocols and examine the pros and cons of this approach.

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#36 • Monday Nov 5, 2018 • Subscriber-only

Advanced Protocol Witnesses: Part 2

We complete our dictionary for translating Swift protocol concepts into concrete datatypes and functions. This includes protocol inheritance, protocol extensions, default implementations and protocols with associated types. Along the way we will also show how concrete types can express things that are currently impossible with Swift protocols.

#35 • Monday Oct 29, 2018 • Subscriber-only

Advanced Protocol Witnesses: Part 1

Now that we know it’s possible to replace protocols with concrete datatypes, and now that we’ve seen how that opens up new ways to compose things that were previously hidden from us, let’s go a little deeper. We will show how to improve the ergonomics of writing Swift in this way, and show what Swift’s powerful conditional conformance feature is represented by just plain functions.

#34 • Monday Oct 22, 2018 • Subscriber-only

Protocol Witnesses: Part 2

Last time we covered some basics with protocols, and demonstrated one of their biggest pitfalls: types can only conform to a protocol a single time. Sometimes it’s valid and correct for a type to conform to a protocol in many ways. We show how to remedy this by demonstrating that one can scrap any protocol in favor of a simple datatype, and in doing so opens up a whole world of composability.

#33 • Monday Oct 15, 2018 • Subscriber-only

Protocol Witnesses: Part 1

Protocols are a great tool for abstraction, but aren’t the only one. This week we begin to explore the tradeoffs of using protocols by highlighting a few areas in which they fall short in order to demonstrate how we can recover from these problems using a different tool and different tradeoffs.

#32 • Monday Oct 1, 2018 • Subscriber-only

Decodable Randomness: Part 2

This week we compare our Decodable solution to building random structures with a composable solution involving the Gen type, exploring the differences and trade-offs of each approach. Along the way we’ll rediscover a familiar old friend with a brand new application.

#31 • Monday Sep 24, 2018 • Subscriber-only

Decodable Randomness: Part 1

This week we dive deeper into randomness and composition by looking to a seemingly random place: the Decodable protocol. While we’re used to using the Codable set of protocols when working with JSON serialization and deserialization, it opens the opportunity for so much more.

#30 • Monday Sep 17, 2018 • Subscriber-only

Composable Randomness

Randomness is a topic that may not seem so functional, but it gives us a wonderful opportunity to explore composition. After a survey of what randomness looks like in Swift today, we’ll build a complex set of random APIs from just a single unit.

#29 • Monday Sep 10, 2018 • Free Episode

DSLs vs. Templating Languages

Templating languages are the most common way to render HTML in web frameworks, but we don’t think they are the best way. We compare templating languages to the DSL we previously built, and show that the DSL fixes many problems that templates have, while also revealing amazing compositions that were previously hidden.

#28 • Monday Sep 3, 2018 • Subscriber-only


This week we apply domain specific languages to a very real-world problem: representing and rendering HTML. We code up a simple but powerful solution that forms the foundation of what we use to build the Point-Free website.

#27 • Monday Aug 27, 2018 • Subscriber-only

Domain Specific Languages: Part 2

We finish our introduction to DSLs by adding two new features to our toy example: support for multiple variables and support for let-bindings so that we can share subexpressions within a larger expression. With these fundamentals out of the way, we will be ready to tackle a real-world DSL soon!

#26 • Monday Aug 20, 2018 • Subscriber-only

Domain Specific Languages: Part 1

We interact with domain specific languages on a daily basis, but what does it take to build your own? After introducing the topic, we will begin building a toy example directly in Swift, which will set the foundation for a future DSL with far-reaching applications.

#25 • Monday Aug 6, 2018 • Free Episode

The Many Faces of Zip: Part 3

The third, and final, part of our introductory series to zip finally answers the question: “What’s the point?”

#24 • Monday Jul 30, 2018 • Subscriber-only

The Many Faces of Zip: Part 2

In part two of our series on zip we will show that many types support a zip-like operation, and some even support multiple distinct implementations. However, not all zips are created equal, and understanding this can lead to some illuminating properties of our types.

#23 • Monday Jul 23, 2018 • Subscriber-only

The Many Faces of Zip: Part 1

The zip function comes with the Swift standard library, but its utility goes far beyond what we can see there. Turns out, zip generalizes a function that we are all familiar with, and it can unify many seemingly disparate concepts. Today we begin a multipart journey into exploring the power behind zip.

#22 • Monday Jul 16, 2018 • Free Episode

A Tour of Point-Free

Join us for a tour of the code base that powers this very site and see what functional programming can look like in a production code base! We’ll walk through cloning the repo and getting the site running on your local machine before showing off some of the fun functional programming we do on a daily basis.

#21 • Monday Jul 9, 2018 • Subscriber-only

Playground Driven Development

We use Swift playgrounds on this series as a tool to dive deep into functional programming concepts, but they can be so much more. Today we demonstrate a few tricks to allow you to use playgrounds for everyday development, allowing for a faster iteration cycle.

#20 • Monday Jun 25, 2018 • Subscriber-only


We often deal with collections that we know can never be empty, yet we use arrays to model them. Using the ideas from our last episode on algebraic data types, we develop a NonEmpty type that can be used to transform any collection into a non-empty version of itself.

#19 • Monday Jun 11, 2018 • Subscriber-only

Algebraic Data Types: Generics and Recursion

Our third installment of algebraic data types explores how generics and recursive data types manifest themselves in algebra. This exploration allows us to construct a useful, precise type that can be useful in everyday programming.

#18 • Monday Jun 4, 2018 • Subscriber-only

Dependency Injection Made Comfortable

Let’s have some fun with the “environment” form of dependency injection we previously explored. We’re going to extract out a few more dependencies, strengthen our mocks, and use our Overture library to make manipulating the environment friendlier.

#17 • Monday May 28, 2018 • Subscriber-only

Styling with Overture

We revisit an old topic: styling UIKit components. Using some of the machinery we have built from previous episodes, in particular setters and function composition, we refactor a screen’s styles to be more modular and composable.

#16 • Monday May 21, 2018 • Subscriber-only

Dependency Injection Made Easy

Today we’re going to control the world! Well, dependencies to the outside world, at least. We’ll define the “dependency injection” problem and show a lightweight solution that can be implemented in your code base with little work and no third party library.

#15 • Monday May 14, 2018 • Subscriber-only

Setters: Ergonomics & Performance

Functional setters can be very powerful, but the way we have defined them so far is not super ergonomic or performant. We will provide a friendlier API to use setters and take advantage of Swift’s value mutation semantics to make setters a viable tool to bring into your code base today.

#14 • Monday Apr 30, 2018 • Subscriber-only


Let’s explore a type of composition that defies our intuitions. It appears to go in the opposite direction than we are used to. We’ll show that this composition is completely natural, hiding right in plain sight, and in fact related to the Liskov Substitution Principle.

#13 • Monday Apr 23, 2018 • Subscriber-only

The Many Faces of Map

Why does the map function appear in every programming language supporting “functional” concepts? And why does Swift have two map functions? We will answer these questions and show that map has many universal properties, and is in some sense unique.

#12 • Monday Apr 16, 2018 • Subscriber-only


We typically model our data with very general types, like strings and ints, but the values themselves are often far more specific, like emails and ids. We’ll explore how this can lead to subtle runtime bugs and how we can strengthen these types in an ergonomic way using several features new to Swift 4.1.

#11 • Monday Apr 9, 2018 • Subscriber-only

Composition without Operators

While we unabashedly promote custom operators in this series, we understand that not every codebase can adopt them. Composition is too important to miss out on due to operators, so we want to explore some alternatives to unlock these benefits.

#10 • Tuesday Mar 27, 2018 • Free Episode

A Tale of Two Flat-Maps

Swift 4.1 deprecated and renamed a particular overload of flatMap. What made this flatMap different from the others? We’ll explore this and how understanding that difference helps us explore generalizations of the operation to other structures and derive new, useful code!

#9 • Monday Mar 26, 2018 • Subscriber-only

Algebraic Data Types: Exponents

We continue our explorations into algebra and the Swift type system. We show that exponents correspond to functions in Swift, and that by using the properties of exponents we can better understand what makes some functions more complex than others.

#8 • Monday Mar 19, 2018 • Subscriber-only

Getters and Key Paths

Key paths aren’t just for setting. They also assist in getting values inside nested structures in a composable way. This can be powerful, allowing us to make the Swift standard library more expressive with no boilerplate.

#7 • Monday Mar 12, 2018 • Subscriber-only

Setters and Key Paths

This week we explore how functional setters can be used with the types we build and use everyday. It turns out that Swift generates a whole set of functional setters for you to use, but it can be hard to see just how powerful they are without a little help.

#6 • Monday Mar 5, 2018 • Subscriber-only

Functional Setters

The programs we write can be reduced to transforming data from one form into another. We’re used to transforming this data imperatively, with setters. There’s a strange world of composition hiding here in plain sight, and it has a surprising link to a familiar functional friend.

#5 • Monday Feb 26, 2018 • Subscriber-only

Higher-Order Functions

Most of the time we interact with code we did not write, and it doesn’t always play nicely with the types of compositions we have developed in previous episodes. We explore how higher-order functions can help unlock even more composability in our everyday code.

#4 • Monday Feb 19, 2018 • Free Episode

Algebraic Data Types

What does the Swift type system have to do with algebra? A lot! We’ll begin to explore this correspondence and see how it can help us create type-safe data structures that can catch runtime errors at compile time.

#3 • Monday Feb 12, 2018 • Free Episode

UIKit Styling with Functions

We bring tools from previous episodes down to earth and apply them to an everyday task: UIKit styling. Plain functions unlock worlds of composability and reusability in styling of UI components. Have we finally solved the styling problem?

#2 • Monday Feb 5, 2018 • Free Episode

Side Effects

Side effects: can’t live with ’em; can’t write a program without ’em. Let’s explore a few kinds of side effects we encounter every day, why they make code difficult to reason about and test, and how we can control them without losing composition.

#1 • Monday Jan 29, 2018 • Free Episode


Our first episode is all about functions! We talk a bit about what makes functions special, contrasting them with the way we usually write code, and have some exploratory discussions about operators and composition.

#0 • Monday Jan 29, 2018 • Free Episode

We launched!

Point-Free is here, bringing you videos covering functional programming concepts using the Swift language. Take a moment to hear from the hosts about what to expect from this new series.

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